Charge for gas pressure operated blasting devices



Patented Apr. 11, 1939 UNITED STATES PATENT OFFICE CHARGE FOR GASPRESSURE OPERATED BLAST'ING DEVICES No Drawing. Application September 2,1937, Se-

rlal No. 162,221. In Great Britain September Claims.

This invention relates to pressure operated blasting devices and inparticular to charges for such devices.

There are now on the market blasting devices which consist of a cylinderhaving at one end a seal which gives way when the pressure inside thecylinder reaches a certainvalue. The cylinder is charged with acomposition or a liquid such as liquid carbon dioxide which evolves gason being heated and a heater is placedin contact with the charge. Thewhole cylinder is placed in a bore hole and the heater ignited. Whensuflicient gas has evolved to bring the pressure to the desired value,the seal gives way and the pressure is released into the bore hole withexplosive violence.

In my specification Serial No. 68,143 filed March 10, 1936, I use, as acharge for a gas-pressure operated device, a gas-evolving compositionconsisting essentially or largely of ammonium nitrate sensitised by thepresence of a suitable chromium compound so as to be capable ofundergoing a self-sustained decomposition without detonation whenignited locally at ordinary pres- 25 sure, and a suitable local andlimited nondetonating igniting element. The igniting element isinsumcient in itself to produce any appreciable rise in temperature ofthe whole of the ammonium nitrate composition, but heats a portion 30 ofthe composition in its immediate vicinity sufflciently to start itsexothermic decomposition. the heat evolved from the exothermicdecomposition being sufiicient to raise more of the composition in itsimmediate vicinity from ordinary temperature to the point ofdecomposition, and so forth; so that the decomposition is propagatedthroughout the whole composition. For blasting purposes the charge iscontained in a pressure-resistant vessel sealed with a pressure-re- 40sponsive venting device; and owing to the eflect of the confinement onits rate of propagation, the decomposition becomes rapid, so that theblast due to the escape of the gases through the venting device takesplace at only a short inposition in order to avoid this objectionableformation of acid fumes.

The increased exothermicity of a mixture containing an oxldisablematerial over that of a mixture' of only the ammonium nitrate and thechromium compound naturally depends on the amount and nature of theoxidisable material. The tendency is for the sensitiveness to ignitionand selfsustained decomposition on local heating in the unconfined stateto increase with an increase in the proportion of carbonaceous materialin the mixture from the amount resulting in the formation of carbondioxide to that resulting in the formation of carbon monoxide.

According to my said specification there are used combustiblecarbonaceous ingredients. Such normally incombustible oxidisablecarbonaceous materials as ammonium carbonate or bicarbonate, which onthermal decomposition absorb heat and evolve unobjectionable gaseousproducts are also used according to my said specification as materialscapable of oxidation by the ammonium nitrate, although only inconjunction with normally combustible carbonaceous ingredients.

For the purpose of blasting in fiery or dusty mines it is obviouslynecessary that the products of combustion vented from the blastingdevice should not be capable of igniting a fiery or dusty atmosphere,and that no flame should accompany their ejection.

For blasting purposes in general it is preferred that the proportions ofammonium nitrate and oxidisable material should be such that little orno carbon monoxide is formed among the products of combustion, andaccording to my said specification it is therefore. considerableparticularly desirable for the purposes of blasting in fiery or dustymines that the proportions of ammonium nitrate and oxldisable materialshould be so adjusted that the carbonaceous materials present arepractically completely burnt to carbon dioxide and water, in addition tothe requirements that the charge should cause no ignition on ejection.

As regards the ignition of fiery or dusty atmospheres it is not merelynecessary that the products of complete combustion should be incapableof igniting the atmosphere, but it is also necessary that no suchignition should occur as a result of the election of flaming gases oronly partlylreacted portions of the mixture in a state of excessivetemperature or liability to burst into flame on election. The failure toful fll these conditions may thus lead to an ignition if a charge inexcess of that necessary to effect venting is employed.

On a superficial examination of the problem it might appear that theseobjects can be accomplished while avoiding on the one hand theinconvenience of excessive evolution of hot oxides of nitrogen or nitricacid and on the other hand the inconvenience of excessive evolution ofcarbon monoxide with a mixture consisting of ammonium nitrate andcombustible carbonaceous materials merely by accurately adjusting thequantities of the ingredients of the mixture so that there would bepresent neither so much ammonium nitrate as to give rise to nitric acidor nitrous fumes, or so much combustible carbonaceous material as togive rise to carbon monoxide.

While a mixture of sensitised ammonium nitrate and combustiblecarbonaceous ingredients in such proportions is capable of completereaction under confinement to form products of combustion objectionableeven from the point of view of ignition of fiery or dusty atmospheres,such a mixture burns in the open with flame. There is thus a danger thatsome of the still incompletely reacted or unreacted mixture will bevented in a flaming condition with the blast. The fact that the abovemixture burns in the open with flame constitutes a further disadvantagein that it would not be premissible to keep a supply of such a mixturein the fiery or dusty atmosphere of the mine since an accidental localrise in temperature might bring about the initiation and the propagationof a decomposition through the material and thus would, on account ofthe fact that the mixture burns with flame, lead to an ignition in themine.

The present invention has as an object to provide a charge which willavoid on the one hand the inconvenience of excessive evolution of hotoxides of nitrogen and nitric acid from the blasting device and on theother hand the inconvenience of excessive evolutionof carbon monoxide,while at the same time avoiding the danger of igniting a fiery or dustyatmosphere. Further objects of the invention include the provision of animproved charge for operating blasting devices of the type describedwhich comprise sensitised ammonium nitrate mixture which do not burnwith flame even in the open, the provision of charges comprisingsensitised ammonium nitrate compositions of satisfactory utility inblasting in conjunction with a complementary charge element but whichare not themselvescapable of propagating their decomposition in the openon subjection to limited and local application of heat. Further objectswill appear hereinafter.

In my specification 68,143 I indicated that the combustible carbonaceousingredient of a sensitised ammonium nitrate combustible carbonaceousingredient mixture might be subjected to a flreproofing treatment. Theadvantage thatthe mixture so prepared was nolonger liable to burn withflame in the open would. in this case depend entirely on theeifectiveness' of the flreproofing treatment, and local imperfections.might have exceedingly serious consequences in the case of a quantityof the material in the mine locally subjected to an accidentalapplication of heat so as to bring about propagation of thedecomposition through the material in the open mine. Moreover, theejection during the blast of the extremely hot particles. of solidinorganic flreproofing agent mightin itself tend to cause the ignitionof inflammable gases, apart from any question of the failure of theflreproofing process to be effective throughout each and every particleof carbonaceous ingredient, which would not only render it inadvisableto keep the material in the open mine for the reasons given in thepreceding sentence, but would also constitute a risk during the ejectionof partly; reacted material.

I therefore considered it necessary to employ some material asoxidisable ingredient which did not yield so high an evolution of heatas combustible carbonaceous ingredients. I found it convenient to makeuse according to my said specification of such materials as ammoniumcarbonate or bicarbonate as were oxidisable by ammonium nitrate,incombustible under ordinary circumstances, and yielded a smallerevolution of heat on their oxidation with ammonium nitrate than thatyielded by normally combustibleif used in excess of the amount capableof oxi dationby the ammonium nitrate, would further function as activecooling agents. Mixtures consisting entirely of ammonium nitrate andsuch normally incombustible ingredients however even when sensitised bythe presence of the chromium compound are insufliciently sensitive toundergo a self-propagating decomposition when subjected to the action ofthe igniting element.

This disadvantage I proposed to overcome in specification 68,143by stillkeeping in the mixture a sufllcient percentage of normally combustiblecarbonaceous material, the greater heat evolution of which on oxidationby the ammonium nitrate naturally increased the sensitiveness of themixture to ignition. A compromise was thus effected between insuflicientsensitiveness and the risk of causing ignition of fiery or dustyatmospheres.

The inclusion of small proportions of fixed alkaline materials in thesensitised ammonium nitrate mixture was also shown in specification"bustible carbonaceous material suflicient to render itselfvpropagating.

Although by application of the principles indicated in the precedingparagraphs in a meticulous fashion it was possible to strike acompromise and so v prepare satisfactory blasting charges for use infiery or dusty mines according to my said specification, I have nowfound that by the application of a newer different principle it ispossible toensure certainty of propagation of :the charge in theblasting device and a freedom from the risk of igniting a fiery or dustyatmosphere independent of flreproofing processes, which is not merelysuflicient to ensure that a properly charged blastingdevice will effecta blast without the risk of ignition, but

such that the ammonium-nitrate mixture is itselfincapable of burningwith a flame. The

.range .ofavailable ammonium-nitrate compositions is now greatlyincreased, and the present invention has the advantage that it ispossible to employ as ammonium-nitrate mixtures not merely mixtureswhich do not burn with flame in the open, but mixtures which do not evenpropagate their decomposition outside the blasting device in the openwhen subjected to a local and limited application of heat. Thisconstitutes an efiicae cious safeguard against the possibility of anaccidental local rise in temperature in a quantity of the mixture keptin the mine leading to any mishap.

The principle on which my present invention depends is that thecombustible carbonaceous ingredients of a sensitised ammonium nitratecharge for a blasting device of the kind described need not of necessitybe evenly scattered throughout the whole of the charge, but will performtheir functions if they are segregated in one part of it. According tomy invention at least a portion of the combustible carbonaceousingredient is segregated from the remaining mixture in coherent integralform, as contrasted with the disintegrated form in which it is presentin the mixture, and at least partly in the neighborhood of the igniter.

The principle of the present invention is compatible in application withthe principles applied according to my specification 68,143. Thus inputting my invention into effect the segregated or unsegregatedcarbonaceous material may be fireproofed; the mixture may contain aproportion of fixed alkaline material; and normally incombustibleoxidizable ingredients such as ammonium carbonate and bicarbonate may bepresent in the mixture as part of the material oxidizable by theammonium nitrate or as a cooling agent. Thus the mixture and thesegregated carbonaceous ingredient function in the closed blastingdevice in complementary fashion, but the ammonium nitrate mixture itselfcontains too little carbonaceous combustible ingredient to render itcapable of burning with flame in the open irrespective of anyfireproofing treatment, and need not possess the property of being ofitself capable of propagating its decomposition when enclosed with alocal and limited igniter in the absence of the complementary segregatedcarbonaceous combustible material. The segregated carbona ceous materialmay conveniently be associated with the igniter as a unit and it isconvenient to form the segregated carbonaceous material as a paper tubeor the like in which the igniter itself may be located. It is preferableto locate the igniter some distance away .from both ends of the blastingdevice, that is to say from the venting' end and from the end mostremote therefrom. Thus there may be used a paper tube of considerablelength within which the igniter is positioned about half way along-theblasting device. This prevents the igniter hurling the whole of themixture against the seal, which might prematurely break it.

In adjusting the quantities of the ingredients so that neither excess ofoxidizable or oxidizing agent is present, account should be taken of theoxidizable ingredients of both the igniter, and the segregatedcarbonaceous ingredient as well as the oxidizable ingredients in themixture.

Since it is desirable that the amount of oxidizable material in thecharge should be restricted so that little or no free carbon monoxide isformed, the nature of the igniting element should be taken into accountin the determination of the weight of carbonaceous material that must beincluded as a charge constituent segregated from the sensitised ammoniumnitrate composition. For example, in the case of a IOU-grain powder fusethe products of combustion of the black-powder are capable of reducingabout 9 grams ammonium nitrate, and the sealing material, employed andthe paper container and its waterproofing material also consume anamount of ammonium nitrate dependent upon their nature and weight. Atypical 30-grain electric fuse, provided with polychlor-naphthaleneplugs amounting to 1.4 grams and a waxed paper container weighing about1.1 grams, consumes in all about 18.5 grams ammonium nitrate;but as itwould normally be constructed a local and limited igniting element wouldnot consume more than 30 to 35 grams ammonium nitrate. According to thepresent invention it may be necessary in the case of large charges tosegregate an amount of carbonaceous material equivalent to as muchammonium nitrate again as will oxidise an igniter of such constructionin order to preserve a satisfactory margin of safety; and even in thecaseof smaller charges the segregation of an amount of carbonaceousmaterial from the composition equivalent to a greater amount of ammoniumnitrate than could be reduced by such an igniter alone renders possiblethe use of compositions having a greater margin of safety than those inwhich the same proportion of carbonaceous ingredient, excluding theigniter, is distributed throughout the composition.

In putting my invention into effect, I may use the segregatedcarbonaceous material in the form of a paper or thin cardboardstructure, as for instance a tube, and this may be impregnated with waxor the like. If desired, the structure may be made up integral with anigniting element such as an electric powder fuse by attachment of thelatter thereto so that it projects for some distance into the blastingdevice; and one or both of the lead-wires may conveniently be passedthrough the tube from the igniter to their terminals in the device. Anextended tube of the carbonaceous material suitably sealed may also beemployed wholly or in part as a container for the active charge in theigniting element. For example, we may employ, in conjunction with thesensitized ammonium nitrate composition, a 100- grain powder fuse madeup in an extended paper or thin cardboard container, suitably sealed andwaterproofed, which itself provides the necessary weight of segregatedcarbonaceous material. As waterproofing agent, paraflln wax or the likemay be employed; and if desired the cementitious ingredient employed forinsulating the leads to the fusehead and for sealing the activecomposition within the igniting element may consist of an organicinsulating material, for example a chlorinated naphthalene wax, insteadof sulphur. The

segregated carbonaceous material may also be,

constructed in forms other than tubular, and may consist of materialsother than paper or cardboard capable of effective segregation from thesensitized ammonium nitrate composition, so that it will not bedistributed to any substantial extent through the latter by the slightdisruptive action of the igniting element. As a further precaution, thesegregated carbonaceous material may if desired be subjected to aflameproofmg treatment. When the segregated carbonaceous material ismade up under these conditions in the form of a container for the activecomposition of the igniting element, any fragmentation incidental to theactuation of the igniting element does not in practice render anysensitized ammonium nitrate composition ejected from the blasting deviceafter venting capable of causing an ignition in fiery or dustyatmospheres; and 1' have also been able to include at least a part ofthe segregated carbonaceous material in the form of small pieces ofwood, charcoal, cardboard or the like, along with the active compositionof the igniting element in its container without detriment to the safetyof the charge as a whole.

The invention is further illustrated but not limited by the followingexamples, in which the parts are parts by weight unless otherwisestated.

Example 1 The blasting device used has a capacity of 680 cc., and ventsat an internal pressure of 12 tons per square inch. The charge consistsof 140 grams of a composition containing a mixture of ammonium nitrate,ammonium dichromate, starch and china clay in the proportions :5:2 :3;and an extended igniter containing grains of blackpowder, which is madefrom a tube of waxed fireproof paper 22" long weighing 13.8 grams, thecementing ingredient used for sealing and insulating being a. wax-likechlorinated naphthalene and weighing 2.4 grams. About half the length ofthe tube forms the actual container for the powder charge, the remainderenclosing the lead-wires. The above weight of composition is in excessof the amount required to generate the venting pressure. On ignition,the blast takes place without the development of objectionable nitrousfumes, and when the device is vented into a 9% methane-in-air atmosphereno ignition of the gas takes place, The amount of ammonium nitrate inthe composition which is not reduced by the starch amounts to 106 grams,and the ammonium nitrate consumption of the igniter assembly containingthe segregated carbonaceous material is in all 110 grams.

Example 2 The blasting device has a capacity of 660 cc. and vents at 21tons per square inch internal pressure. The composition used in thecharge consists of 280 grams of a mixture of ammonium nitrate, ammoniumdischromate, starch, charcoal, china clay, basic magnesium carbonate andammonium bicarbonate in the proportions 80:6:2:1:1:5:20. The segregatedcarbonaceous material is in the form of an igniter tube 9% inches longof fireproofed paper waterproofed with Wax and weighing 6.8 grams, intowhich a fusehead and 100 grains of blackpowder are sealed with 2.4 gramsof a chlorinated naphthalene wax. The ammonium nitrate in thecomposition not reduced by the starch and ammonium bicarbonate amountsto approximately 67 grams, the total ammonium nitrate consumption of theigniter .assembly being 70 grams; this charged device is also safe whenoperated in gas and evolves no offensive nitrous fumes. I

Example 3 The blasting device has a capacity of 680 cc. and vents at 12tons per square inch internal pressure. The composition consists of 210grams of a mixture of ammonium nitrate, ammonium dichromate, starch,ammonium bicarbonate, basic magnesium carbonate and china clay in theproportions 80:6:3:20:3:1. The segregated carbonaceous material takesthe form of a tube 9 inches long of flreproofed paper weighing 2.8grams, into which a fusehead and 100 grains blackpowder are sealed with2.4 grams of a chlorinated naphthalene wax. The igniter has a totalammonium nitrate consumption of about 45 grams. The ammonium nitrateunreduced in the composition amounts to 59 grams, No objectionablenitrous fumes are however produced, and the charged device is safe whenoperated in gassy and fiery atmospheres.

In addition to the oxidisable ingredients according to my saidspecification small proportions of inorganic materials such as magnesiumcarbonate, chalk, silica, china clay or the like which influence thedecomposition of ammonium nitrate may be included, and any combustibleorganic ingredients present in the mixture may be fireproofed in orderto minimise the risk of any such ingredients being vented whileunconsumed or only partly consumed.

Suitable igniting elements are: an electric powder fuse as used forigniting blackpowder pellets, a safety electric igniter as described inspecification 431,950, or a small smokeless powder or cordite chargeignited in turn by a fuse head or percussion cap, and the use of 30 to100 grain powder fuses is illustrated.

The total quantity of carbonaceous ingredients in the charge and ignitertaken together depends on the quantity of noncombustible ingredientswhich are oxidisable with ammonium nitrate and will vary with thechemical composition of such ingredients.

The proportion of combustible carbonaceous ingredients admixed in theammonium nitrate should never exceed 4% and I prefer to keep it below 3%of the weight of ammonium nitrate and the remainder should besegregated. The total amount together with the other oxygen us- 'ingingredients should be, as has been stated,

such that neither nitrous fumes nor carbon mondevices of the type whichcomprises an igniter and ammonium nitrate sensitised with a chromiumcompound, carbonaceous substances which combine exothermically withoxygen, cooling salts in a quantity consistent with certain propagationof the decomposition of the ammonium nitrate, and in which the totalquantities of all the ingredients present both in the igniter and in therest of the charge are adjusted substantially to the theoreticalquantities necessary to their decomposition without the formation ofoxides of nitrogen, nitric acid, and carbon monoxide and without therebeing left any unburnt carbonaceous material; the modification that thequantity of carbonaceous substances, which combine exothermically withoxygen, distributed 3. The modification as claimed in claim 1 in whichthe carbonaceous substances are fireproofed. I

4. A modified charge as claimed in claim 1 in which the segregatedcarbonaceous substances comprise a blackpowder igniter enclosed in P p5. The modification as claimed in claim l in which the segregatedcarbonaceous material is placed in the neighborhood of the igniter.

6. The modification as claimed in claim 1 in which the segregatedcarbonaceous material is placed away from the vent hole.

'7. The modification as claimed in claim 1 in which the segregatedcarbonaceous material is included in the igniter,

8. The modification as claimed in claim 1 in which the segregatedcarbonaceous material is partly included in the igniter and theremainder is segregated in coherent form.

9. In a charge for pressure-operated blasting devices of the type whichcomprises an igniter and ammonium nitrate sensitized with a chromiumcompound, carbonaceous substances which :ombine exothermically withoxygen, cooling salts in a quantity consistent with certain propagationof the decomposition of the ammonium nitrate, and in which the totalquantities of all the ingredients present both in the igniter and in therest of the charge are adjusted substantially to the theoreticalquantities necessary to their decomposition without the formation ofoxides of nitrogen, nitric acid, and carbon monoxide and without therebeing left any unburnt carbonaceous material; the modification that asubstantial portion of saidcarbonaceous substances is segregated fromthe remainder of the charge.

to their decomposition without the formation of oxides of nitrogen,nitric acid, and carbon monoxide and without there being left any unbumtcarbonaceous material; the modification that a substantial portion ofsaid carbonaceous substances is segregated from the remainder of thecharge.

JAMES TAYLOR.

April 11, 1959.

JAMES TAYLOR.

It is hereby certified that error appears in the printed specificationof the above numbered patent requiring correction as follower Page 2,first column, line 22, for the word objectionable read'unobjectionable;page 1 first column, line hh, for "dischromte" read dichrbniate; andthat the said Letters Patent should be read with this correction thereinthat the same may conform to the record of the case in the PatentOffice.

Signed and sealed this th day of June, A. D. 19 9.

(Seal) Henry Van Arsdale Acting Commissioner of Patents.

